In recent years, vehicle-mounted devices have been developed which can utilize DSRC (Dedicated Short Range Communication) to perform dedicated short range communication with a roadside apparatus installed on a road to receive information provided by a center apparatus, via the roadside apparatus.
As a system using such a vehicle-mounted device, an ETC (Electronic Toll Collection System) is known in which a transmission and reception antenna provided at a toll gate communicates wirelessly with a vehicle including a vehicle-mounted device with an automatic toll collection function, in order to automatically collect the toll without the need to temporarily stop the vehicle. In the ETC technique, a problem of leakage of electric waves in the communication area of the transmission and reception antenna has arisen.
Thus, as a technique for preventing the leakage of electric waves in the ETC, for example, an electric wave absorber has been disclosed which includes an electric wave absorber member and an electric wave absorption assist member in order to suppress the leakage of electric waves in the communication area of the transmission and reception antenna (see Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-237719